It is known that the pH value in the gastric apparatus of monogastric animals is acidic. The pH value varies according to the specific portion of the gastrointestinal tract. For example, the stomach has a pH of 2 to 5, the duodenum has a pH of 4 to 6, the jejunum has a pH of 6 to 7, the cecum has a pH of 6 to 6.5 and, finally, the colon a pH of 6.5 to 7.
In the gastrointestinal system said acid environment provides a protective effect against the proliferation of pathogens.
It is known, however, that some pathogenic organisms are capable of developing a complex defence system which enables the cells of the pathogens themselves to survive even where the pH values fall to as low as 3. Moreover, some bacteria, such as Salmonella typhimurium, may develop a system able to tolerate acids with a pH of 3 after previous exposure to a weak acid with a pH of 5.